1. Field of the Invention
The present invention relates to a method for producing a printed wiring board, and to a printed wiring board produced through the method. More particularly, the invention relates to a novel method for smoothing the surface of a printed wiring board, and to a smoothed printed wiring board produced through the smoothing method.
2. Background Art
Conventionally, solder-resist-covered printed wiring boards are produced through applying a photo- and heat-curable solder resist ink to the entire surface of a printed wiring substrate; exposing the solder resist ink layer to light via a negative-image mask for masking the circuit, to thereby cure the solder resist; removing the light-unexposed portion on the circuit through development; and completely curing the cured light-exposed portion. For example, Japanese Patent Application Laid-Open (kokai) No. 2008-294406 discloses such a process.
However, the printed wiring boards produced through such a conventional method generally have a drawback in that the surface of each printed wiring board in an area between circuit traces is depressed (see FIG. 3).
One approach for overcoming this drawback includes applying an undercoat ink onto the entire surface of the printed wiring substrate and curing the ink; polishing the cured undercoat layer until the circuit is exposed to thereby smooth the surface (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2006-108163, FIG. 3); and applying the aforementioned conventional production method to the smoothed printed wiring substrate, to thereby produce a solder-resist-covered printed wiring board.
However, when this approach is employed, the circuit may be undesirably removed during surface polishing, resulting in damage and wear of the circuit. Furthermore, productivity problematically lowers due to addition of the surface-polishing step.